Wall Street legend stepped down as chairman of Citigroup last April; abdicated seat to Chief Charles Prince. "Sandy" got start earning $35 a week as runner for Bear Stearns in 1956. President of American Express by 1985. Made tidal wave on Wall Street in 1998; convinced Citicorp to merge with his insurance hodgepodge Travelers Group; created Citigroup, now world's largest financial services company. Rumors he planned to create a $5 billion private equity fund with Saudi Prince Alwaleed unfounded. Now giving fortune away. Plans to improve high schools via National Academy Foundation, a nonprofit group that introduces inner-city kids to the world of business.